Blind rivet and method of making the same

ABSTRACT

Disclosed is a self plugging blind rivet for securing together apertured members, the rivet comprising a tubular shell having a tail end face at one end and a preformed radially enlarged bead at the other end, and a stem that extends through the shell and has a stem head adjacent the tail end face of the shell and a breakneck located away from the stem head, in which the region of the stem shank on the stem head side of the breakneck has a plurality of depressions formed therein extending to the breakneck, the corresponding region of the shell substantially filling the depressions in a region adjacent the stem head and progressively less towards the breakneck whereby, in use and under axial compression loading of the shell, the shell preferentially buckles in the region adjacent the member remote from the preformed head to form a blind head in contact with the member so as to clamp together the apertured members. Also disclosed is a method of assembling the above-described rivet comprising inserting the shell in a die, the first part of which closely fits the outside diameter of the shell, a second part being formed as a taper and which progressively increases in diameter until it intersects a third pan of the die into which the tail end of the shell protrudes, supporting the head of the shell with an abutment inserting a punch which has a first diameter closely fitting the bore of the rivet shell and a second diameter which closely fits the third pan of the die, applying a compressive force between the punch and the abutment so as to compress the rivet shell to fill both the taper and the larger diameter of the die, removing the abutment and punch, inserting a stem and ejecting the assembled shell and stem through the die, whereby, during ejection, the material of the shell is forced into the depression in the stem to substantially fill the depressions at least at the tall end of the shell and progressively towards the breakneck.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a blind rivet. A blind rivet is one that can beinserted and set by access to one side only of aperture members to beriveted together.

BRIEF SUMMARY OF THE INVENTION

More particularly, the invention relates to a self plugging blind rivetcomprising a tubular shell having a preformed radial head at one end,and a stem extending through the tubular shell and having a stem headadjacent the tail end of the shell. In use, the rivet is inserted, shelltail end first, through the apertures in the members to be riveted untilthe shell head contacts the nearer member and the shell tail protrudesbeyond the further member. In order to set the rivet, the shell head issupported by an abutment and the stem is then pulled so that the stemhead compresses the shell against the abutment and causes axialcontraction of the shell and radial expression of at least part thereofto form a blind head which, together with preformed head, clamps themembers together. At least part of the stem adjacent to its head isretained within the shell to plug the latter after the rivet has beenset. The remainder of the stem (i.e. the tail end remoted from the headthereof) is preferably broken off to avoid protrusion from the shellhead. This is generally effected by providing a breakneck at anappropriate position in the shank of the stem.

A rivet of this type is described in WO 98/23872 and features that areimportant in the performance of such a rivet are described in thatapplication. The application also describes how a rivet can beconstructed in which the portion of the river stem retained in the rivetafter placing fully plugs the bore of the river and breaks flush withthe head of the rivet under all working conditions of sheet thickness.To this end the pintail has reduced diameter relative to the stem shankand the breakneck is formed at the junction of the stem shank and thepintail.

In a first aspect the present invention provides a self plugging blindrivet for securing together apertured members, the rivet comprising atubular shell having a tail end face at one end and a preformed radiallyenlarged head at the other end, and a stem that extends through theshell and has a stem head adjacent the tail end face of the shell and abreakneck located away from the stem head, in which the region of thestem shank on the stem head side of the breakneck has a plurality ofdepressions formed therein extending to the breakneck, the correspondingregion of the shell substantially filling the depressions in a regionadjacent the stem head and progressively less towards the breakneckwhereby, in use and under axial compression loading of the shell, theshell preferentially buckles in the region adjacent the member remotefrom the preformed head to form a blind head in contact with said memberso as to clamp together the apertured members.

The depressions are preferable axial grooves but may also be spiral oreven annular. Especially where the depressions are axial or spiral, thestem shank and the shell may be provided with mutually-cooperating meansto lock them together. Such means may comprise an annular groove formedaround the stem shank, preferably immediately below the stem head, thegroove containing shell material to retain the stem within the shell sothat, before placing, the assembly of stem and shell is locked togetherand the part of the stem retained in the shell after placing is alsolocked to the shell. The groove may have an axial length ofapproximately one half of its diameter.

Preferably, the region of the stem shank having formed therein thedepressions generally has a major diameter which is greater than thediameter of the region remote from the breakneck, whereby the endadjacent the breakneck comprises one or more radially-protrudingshoulders which in use with a placing tool engage the nose of theplacing tool so that the retained part of the stem breaks substantiallyflush with the rivet head throughout the working range of thickness ofthe members being riveted.

Preferably, the cross sectional area and strength of the stem in theregion adjacent the stem head is substantially equal to that of thecylindrical part of the stem. The number of axial depressions may varyfrom a minimum of four depending on the method of manufacture.Preferably the distance across the mouth of the depressions is less thanthe circumferential width of the land areas between.

Preferably, the depressions are produced by a forming process so thatmaterial displaced from the depressions is contained in the landsbetween the depressions resulting in the increased diameter.

According to a further aspect of the invention a method is provided ofassembling a rivet comprising a tubular rivet shell having a preformedradially enlarged heat at one end and a stem comprising a head and ashank which carries a breakneck remoted from the stem head, the regionbetween the stem head and breakneck being formed with a plurality ofdepressions which extend to the breakneck, the method comprisinginserting the shell in a die, a first part of which closely fits theoutside diameter of the shell, a second part is formed as a taper andwhich progressively increases in diameter until it intersects a thirdpart of the die into which the tail end of the shell protrudes,supporting the head of the shell with an abutment, inserting a punchwhich has a first diameter closely fitting the bore of the rivet shelland a second diameter which closely fits the third part of the die,applying a compressive force between the punch and the abutment so as tocompress the rivet shell to fill both the taper and the larger diameterof the die, removing the abutment and punch, inserting a stem andejecting the assembled shell and stem through the die whereby, duringejection, the material of the shell is forced into the depression in thestem to substantially fill the depressions at the tail end of the shelland progressively less towards the breakneck.

Preferably, the external diameter of the shell in the assembled rivet isequal to the diameter of the stem head. To this end the first die boreshould have the same diameter as the stem head, although this may bedifficult to arrange in practice. Consequently it is preferable that thestem head before assembly of the rivet is slightly larger than the firstdie bore so that, when the assembly is ejected, the stem head is sizedto the diameter of the first die bore and hence to the diameter of theshell.

As an alternative to using a separate punch to form the rivet shell tothe shape of the die, it is possible to approximate to this by using thestem in place of the punch to compress the shell against the abutment,thereby substantially filling the die, removing the abutment andejecting the assembled stem and shell through the die.

Embodiments of the invention will now be described by way of example andwith reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section through the shell of the rivet beforeassembly;

FIG. 2 is a side elevation of the stem of a rivet before assembly;

FIG. 3 is a section along the line A-A′ of FIG. 2;

FIG. 4 is a section through a die containing a rivet body beforecommencing the first stage of the assembly process;

FIG. 5 is similar to FIG. 4 but shows the first stage of the assemblyprocess completed;

FIG. 6 is similar to FIG. 5 but shows the stem inserted in the rivet;

FIG. 7 shows the assembly process completed and the assembled rivetejected from the die; and

FIGS. 8 and 9 show sections of the rivet placed in sheets of minimum andmaximum thickness respectively.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, the shell 17 comprises a tubular body 11having a concentric bore 12 and at one end a radially enlarged head 13which carries a counterbore 15. The tail end 16 of the shell is flat andat right angles to the shell axis.

The stem 21 shown in FIG. 2 is elongate and generally cylindrical. Atone end it has an integral radially enlarged head 22 which has convexface 23 directed away from the stem shank 25 and a substantially flatannular face 24 directed towards the stem shank. The diameter of thestem head is larger than the diameter of the body of the shell. Spacedaway from the stem head is a groove 27 which constitutes a breakneckwhich determines the position at which the stem breaks when the rivet isplaced. Breakneck 27 has a tapered force 30 directed towards the stemhead and a face 31 normal to the stem axis directed towards the pintail29. Between the breakneck 27 and the head of the stem 23 the stemcarries axial depressions 32 which end a distance away from the stemhead to produce a plain cylindrical portion 33 the length of which isapproximately one half of the stem diameter and the diameter of which issubstantially the same as the pintail 29. Depressions 32 are produced bya forming process so that the stem material from the depressions formlands 34 between the depressions as shown in FIG. 3 which is a crosssection along the line A-A′ of the stem of FIG. 2. Thus the crosssectional area of the stem in the region of the depressions and itsstrength is substantially unchanged. Lands 34 are arranged to lie on acircle the diameter of which is as close as possible to the bore of therivet shell 12. Furthermore the dimension across the lands 34 isincreased relative to those parts of the stem which do not carrydepressions, viz the plain cylindrical portion 33 and the pintail 29. Inthis example the width of the mouth of the depressions is somewhat lessthan the width of the lands 34. Comparing this stem to that shown inFIG. 3 of WO 98/23872 it is evident that the stem of this applicationmay be formed from a stem shank of uniform diameter whereas the stem inthe previous application requires the pintail to be of a reduceddiameter relative to the plain portion which can only be effected byextrusion of the pintail or some other additional operation duringmanufacture.

FIG. 4 shows a rivet shell 17 placed in a die 40. Die 40 has a smallbore 41 which closely fits the outside diameter of the rivet shell andthe tail of the rivet 18 protrudes into a larger bore 42. Bore 41 andbore 42 are joined by a tapered section of the die 43.

The head of the rivet 13 is supported by a member 44 which closelyconforms to the rivet head and has a central bore 45. Punch 46 isinserted into large bore 42 so that the smaller diameter 47 of the punchenters the bore 12 of the rivet shell in which it is a close fit. Thelarge diameter 48 of the punch enters the larger bore of the die 42 inwhich it is also a close fit.

FIG. 5 shows the completion of the first stage of the assembly. Punch 46is urged towards the support member 44 and the body of the rivet iscompressed so that it completely fills the large bore of the die 42 andthe tapered portion 43.

For the second state of the assembly, punch 46 is withdrawn, member 44is retracted and die 40 together with the formed rivet shell 17 is movedto a second assembly station (FIG. 6). Here stem 21 is inserted. Die 40is now supported by member 50. Compressive force is now applied viapunch 51 which pushes rivet assembly 52 out of the die in the processswaging the tapered section 43 of the rivet into the recesses 32 of thestem which are progressively more filled as the diameter of the taperdecreases, substantially full filling occurring at the narrow end of thetaper 43.

This is shown in FIG. 7. Additionally, the stem head 22 is sized to theexact diameter 58 of the completed assembly. The progressive increase incross section of the rivet shell results in a corresponding increase inshell stiffness so that when the rivet is placed the tail of the rivetalways forms adjacent the members being riveted. This effect is enhancedby the increased work hardening towards the tail of the rivet. FIG. 7also shows how the plain cylinder portion of the stem 33 which forms arecess between the stem head 22 and the increased diameter of the lands34 is filled with shell material and locks stem and shell together.

FIG. 8 shows a rivet set in minimum thickness sheets and FIG. 9 inmaximum thickness sheets numbered 59 and 60 respectively. Rivets areinserted in respective holes 61 and 62 and set with a suitable pullingtool which has an annular anvil 63 which abuts the head and grippingjaws that grip the protruding part of the rivet stem 29. Operating thesetting tool retracts the jaws relative to the anvil. Such setting toolsare well known in the art of blind riveting. The bore 64 of the anvil 63is a close fit on the pintail 29 and the part of the stem carrying theaxial depressions has a sufficient diameter that it cannot pass throughthe bore of the anvil. Thus during placing the stem always breaks at theanvil. Anvil 63 carries a boss 65 of a diameter slightly less than thecounterbore 15 in the rivet head. The stem therefore breaks when itcontacts the boss ensuring the break point is always below the rivethead surface. FIGS. 8 and 9 also show how due to the progressiveincrease in rivet section towards the tail of the rivet the bulb alwaysforms adjacent to the back sheet. Furthermore since the stem is pulledby the same distance before breaking irrespective of sheet thickness thetail shape changes by a minimal amount. Also the tail 66 of the placedrivet is virtually undeformed and hence stem and shell remain lockedtogether.

What is claimed is:
 1. A self plugging blind rivet for securing togetherapertured members, the rivet comprising a tubular shell having a tallend face at one end and a preformed radially enlarged head at the otherend, and a stem that extends through the shell and has a stem headadjacent the tail end face of the shell and a breakneck located awayfrom the stem head, in which the region of the stem shank on the stemhead side of the breakneck has a plurality of depressions formed thereinextending to the breakneck, the corresponding region of the shellsubstantially filling the depressions in a region adjacent the stem headand progressively less towards the breakneck whereby, in use and underaxial compression loading of the shell, the shell preferentially bucklesin the region adjacent the member remote from the preformed head to forma blind head in contact with said member so as to clamp together theapertured member.
 2. A blind rivet according to claim 1, in which therivet shell has a hardness gradient from the tail to the head, the tailbeing harder than the head.
 3. A blind rivet according to claim 1, inwhich the region of the stem shank having depressions formed therein isgenerally of increased diameter relative to the region remote from thebreakneck, whereby the end adjacent the breakneck comprises one or moreradially-protruding shoulders which in use with a placing tool engagethe nose of the placing tool so that the retained part of the stembreaks substantially flush with the rivet head throughout the workingrange of the thickness of the members being riveted.
 4. A blind rivetaccording to claim 1, in which the depressions are axial grooves.
 5. Ablind rivet according to claim 1, in which the depressions are spiral.6. A blind rivet according to claim 1, in which the stem shank and theshell are provided with mutually-cooperating means to lock themtogether.
 7. A blind rivet according to claim 6 in which themutually-cooperating means comprises an annular groove.
 8. A blind rivetaccording to claim 7, in which the groove is formed around the stemshank.
 9. A blind rivet according to claim 7, in which the annulargroove is immediately below the stem head.
 10. A blind rivet accordingto claim 7, in which the groove contains shell material to retain thestem within the shell.
 11. A blind rivet according to claim 7, in whichthe groove has an axial length of approximately one half of itsdiameter.
 12. A blind rivet according to claim 1, in which the crosssectional area and strength of the stem in the region adjacent the stemhead is substantially equal to that of the cylindrical part of the stem.13. A blind rivet according to claim 1, in which the stem shankcomprises at least four depressions.
 14. A blind rivet according toclaim 1, in which the distance across the mouth of the depression isless than the circumferential width of the land areas between.
 15. Ablind rivet according to claim 1, in which the depressions are formedsuch that material displaced from the depression is contained in thelands between the depressions.
 16. A blind rivet according to claim 1,in which the external diameter of the shell in the assembled rivet isequal to the diameter of the stem head.
 17. A method of assembling arivet comprising a tubular rivet shank having a preformed radiallyenlarged heat at one end and a stem comprising a head and a shank whichcarries a breakneck remote from the stem head, the region between thestem head and the breakneck being formed with a plurality of depressionswhich extend to the breakneck, the method comprising inserting the shellin a die, the first part of which closely fits the outside diameter ofthe shell, a second part is formed as a taper and which progressivelyincreases in diameter until it intersects a third part of the die intowhich the tail end of the shell protrudes, supporting the head of theshell with an abutment, inserting a punch which has first diameterclosely fitting the bore of the rivet shell and a second diameter whichclosely fits the third part of the die, applying a compressive forcebetween the punch and the abutment so as to compress the rivet shell tofill both the taper and the large diameter of the die, removing theabutment and punch, inserting a stem and ejecting the assembled shelland stem through the die, whereby, during ejection, the material of theshell is forced into the depressions in the stem to substantially fillthe depressions at least at the tail end of the shell and progressivelyless towards the breakneck.
 18. A method of assembly of a rivetaccording to claim 17, in which the ejection process results in ahardness gradient in the shell shank between the tail and head ends, thetail end being harder than the head end.